If the military force of an international organization is made the object of a military attack by a State, that international organization may be regarded as being entitled to use force in self-defence. However, since the forces of international organizations are generally composed of national contingents which States put at the disposal of the international organizations, the question may be raised as to whether, in case of an armed attack against such forces, the sending State would also be entitled to use force in self-defence to protect its national contingent. This question, which was addressed, albeit in a very cursory manner, in the 2009 Report of the EU Independent International Fact-Finding Mission on the Conflict in Georgia, has to be answered taking into account the status of national contingents as organs of the sending States. By attaching relevance to the contingent's dual status and to the rationale underlying the rule on self-defence, this study argues that whenever the national contingent is made the object of an armed attack the possibility for the sending State to invoke self-defence cannot be excluded. In particular, the invocability of self-defence by the sending State should be admitted in those cases in which the armed attack is clearly aimed at targeting that State.